Quetiapine hemifumarate (ethanol, 2-[2-(4-dibenzo[b,f][1,4]thiazepin-11-yl-1-piperazinyl)ethoxy], (2E)-2-butenedioate (2:1) salt) is an antipsychotic drug deprived of undesired extrapyramidal side effects, that was developed by ICI and was launched on the market in 1997 under the name Seroquel.
Quetiapine is an achiral molecule of formula:

Besides the hemifumarate salt, other salts are known in literature, such as dihydrochloride, maleate, fumarate, oxalate salts, as well as complexes with solvents.
In the art, quetiapine is synthesized starting from dibenzo[b,f][1,4]thiazepin-11(10H)-one (intermediate

By reacting this intermediate with POCl3, 11-chlorodibenzo[b,f][1,4]thiazepine (intermediate (II)) is obtained:

This compound is then reacted with 1-(2-hydroxyethoxy)ethylpiperazine to give the title compound.
The formation of 11-chlorodibenzo[b,f][1,4]thiazepine (intermediate (II)) is a key step of the synthesis process.
EP 0 240 228 of AstraZeneca discloses the preparation of intermediate (II) by reaction of intermediate (I) with POCl3 in the presence of N,N-disubstituted anilines. POCl3 is used as a solvent.
US 2006/063927 of Chemagis describes the reaction of intermediate (I) with POCl3 in an organic solvent at reflux and in the absence of a base.
WO 2006/117700 of Medichem relates to the preparation of intermediate (II) from intermediate (I) with POCl3 in the presence of an organic amine, namely triethylamine, followed by decomposition of POCl3 excess in situ.
WO 2006/135544 of Cambrex discloses the synthesis of intermediate (II) by reaction of intermediate (I) with POCl3 in an organic solvent, namely toluene, in the presence of a trialkylamine such as triethylamine.